1. Field of the Invention
This invention relates generally to an electro-hydraulic control of an automatic transmission, particularly to a control system having active control of pump displacement.
2. Description of the Prior Art
Most current automatic transmissions use a solenoid in conjunction with a regulator & latch valve to control independently the clutches and brakes, which are applied and released to produce the transmission gear ratios. A valve body assembly that includes a solenoid with a regulator & latch valve for this purpose requires many layers to accommodate all of the solenoids and valves. Such a valve body adds cost and size due to the many valve body layers, and it creates hydraulic response time delays due to the multiple stages from solenoid output to regulator valve input to regulator output, which must be controlled. Further, these delays are temperature sensitive.
Conventional automatic transmissions use bleed flows to improve the hydraulic controls performance and repeatability, but these flows result in lost hydraulic power, which power loss is detrimental to fuel economy.
Variable displacement pump controls are indirectly controlled, which can introduce system instability and deliver a fluid flow rate that is much higher than needed by the transmission, further reducing fuel economy.
Most transmissions use a one-way-clutch to produce a synchronous upshift between first gear and second gear. A conventional one-way-clutch is costly and creates internal drag in the transmission.
A need exists in the industry for an electro-hydraulic control that permits a reduction is size of the valve body, reduces the number of valves, improves vehicle fuel economy and shortens the time required to execute gear shifts.